As an OFDM (Orthogonal Frequency Division Multiplexing) transmission method currently being used in the terrestrial digital television broadcast, there is a transmission method standardized in ETSI EN 300 744 issued by the European Telecommunication Standards Institute (see Non-patent Document 1). This standard defines a transmission method for digital video broadcast, which is called DVB-T (Digital Video Broadcasting Terrestrial) standard. Note that the OFDM transmission method is a type of multicarrier transmission methods for performing digital modulation on each of carriers and multiplexing the modulated carriers.
The following shows the overview of the OFDM transmission method based on the DVB-T standard.
The DVB-T standard includes three transmission modes, namely the 2K mode, the 4K mode and the 8K mode. The number of carries used in the OFDM transmission is different for each mode. Specifically, the number of carries used in the 2K mode, the 4K mode and the 8K mode is 1705, 3409 and 6817, respectively. Also, according to the DVB-T standard, a unit time for performing the digital modulation based on the OFDM transmission is called an OFDM symbol. 68 OFDM symbols constitute a frame, and four frames (272 OFDM symbols) constitute a super frame.
According to the DVB-T standard, TPS (Transmission Parameter Signalling) signals for use in notification of transmission parameter information, and two types of reference signals, namely scattered pilot signals (hereinafter called “SP signals”) and continual pilot signals (hereinafter called “CP signals”), are transmitted in addition to the main stream that is chiefly used for transmitting video information. The DVB-T standard allows the transmission parameter information to be set in several patterns, for control of the transmission speed and the robustness of the main stream. The transmitter uses the TPS signals to notify the receiver of the transmission parameter information. The receiver is capable of estimating the channel characteristics, based on the SP signals and the CP signals.
The TPS signals mentioned above are transmitted by carriers that are arranged at prescribed frequencies. Each of the carriers used for the transmission of the TPS signals is called “a TPS carrier”. The number of the TPS carriers used for the transmission of the TPS signals in the 2K mode, the 4K mode and the 8K mode is 17, 34 and 68, respectively. The TPS carriers included in a single OFDM symbol transmit the same bits of the transmission parameter information and so on in parallel. The transmission parameter information has been modulated with the DBPSK (Differential Binary Phase Shift Keying) method. Each OFDM symbol transmits one-bit binary data of the transmission parameter information and so on.
A block including a series of TPS signals for transmitting the transmission parameter information and so on is called a TPS block. In conventional techniques, the TPS block includes 68 TPS signals, and is to be carried by TPS carriers that are included in a single frame (68 OFDM symbols) and have an identical carrier number.
Each TPS block is 68-bit binary data, which includes one initialization bit s0, 16 synchronization word bits s1-s16, 37 transmission parameter information bits s17-s53, and 14 redundancy bits s54-s67 for error protection. The initialization bit s0 is used for initialization of the modulation phase of the DBPSK. The synchronization words s1-s16 are reflected codes consisted of “0011010111101110” or “1100101000010001”, and are used for frame synchronization in the receiver. The transmission parameter information bits s17-s53 includes Length indicator showing the length of information included in the transmission parameter information bits s17-s53, Frame number, Constellation (i.e. the modulation method for the data transmission carriers), Hierarchy information, Code rates for channel coding, Guard intervals for the OFDM transmission, Transmission mode, Cell ID, and reserved bits. The redundancy bits s54-s67 are redundancy codes that have been coded with shortened BCH code (67, 53) with respect to the synchronization word bits s1-s16 and the transmission parameter information bits s17-s53. The receiver is capable of correcting transmission errors of up to 2 bits by using the shortened BCH code (67, 53).
A receiver pertaining to the DVB-T standard acquires the transmission parameter information carried by the TPS signals, and identifies the transmission method (the Constellation, the Hierarchy information, the Code rates for the channel coding, etc.) based on the acquired transmission parameter information. As a result, the receiver can demodulate and decode the main stream. Since the transmission parameter information is important for the demodulation and the decoding of the main stream, the TPS signals have been designed to be robust. For example, since the TPS carriers transmit the same bits included in the TPS block in parallel, the receiver can prevent reception errors by combine and demodulate the same bits included in the TPS block carried by the plurality of TPS carriers. Also, since the TPS signals are carried by the plurality of TPS carriers, the TPS signals have the frequency diversity effect and the robustness against the frequency selective fading.
The receiver establishes the frame synchronization by detecting that the synchronization words s1-s16 are reflective between each two successive frames. Note that the reflective structure of the synchronization words s1-s16 prevents that the frame synchronization is established at an incorrect position even though other data carried by the TPS signals bears a resemblance to the synchronization words.
On the other hand, as a DVB-T-based transmission method for use by mobile terminal apparatuses, DVB-H (Digital Video Broadcasting Handheld) has been standardized. According to the DVB-H standard, the main stream is intermittently multiplexed in DVB-T-based transmissions, and the receiver intermittently receives the main stream. As a result, the DVB-H standard can reduces the power consumption by the receiver.    Non-patent Document 1: ETSI EN 300 744